Universität zu Köln

Aubin, Suzanne Grace (2025). Structure-Property Relationships of Waterborne Polyurethane Dispersions based on Novel Hybrid Components. PhD thesis, Universität zu Köln.

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Abstract

Water-based polyurethane hybrid dispersions (PUHD) are becoming increasingly important in technical applications in the coatings and adhesives industry. These are aqueous PU mixing systems consisting of polyurethane (PU) and other polymeric materials such as acrylate, silicone or fluorine compounds. The result is an improved material performance in respect to the basic PU products, such as mechanical properties, and a good alternative to the usual post-curing with additives required for PUD films. Nevertheless, hybrid synthesis (miniemulsion polymerization, grafting) poses great challenges. The focus of this work is on the synthesis of the hybrid component and its incorporation into the PU framework. Polystyrene (PS) disclose a particularly interesting range of properties due to its high glass transition temperature (Tg). Properties such as segregation phenomena, uncontrolled PS content, molecular weight (Mn) and other negatively influencing parameters due to lack of covalent bonding are circumvented by targeted covalent incorporation of PS blocks into the PU scaffold and should provide insights into structural effects that significantly influence film properties. For this purpose, bifunctional polystyrene (PS(OH)2) is used in the PU reaction. Living polymerization techniques are suitable for the production of such components with tailor-made hydroxyl functionalities. In particular, the Radical Addition Fragmentation Transfer (RAFT) process is one such technique. A new effective RAFT agent based on trithiocarbonate has been kinetically investigated. As a valuable alternative, anionic polymerization initiated with lithium naphtalenide (LiNaph) and terminated with propylene oxide (PO) has been inves-tigated. The optimal reaction conditions of both methods are highlighted, and the PS(OH)2 obtained is extensively characterized. A correlation between Mn and Tg is confirmed. The prepolymer reaction as an essential building block of PUHD synthesis is investigated with respect to the PS(OH)2 content. Both synthesis processes yield polyols with good reactivity towards isocyanates. Finally, the preparation of corresponding PUHDs by the acetone process is investigated. Practical formulations are used. Both PS(OH)2 types are varied according to their content in the dispersion and structure-property effects are studied. It is found that the PS blocks are fully incorporated into the PU framework. A maximum amount of PS(OH)2 is still required to optimize the properties of both components in the PUHD. Overall, the structure-property relationships of PUHDs and their potential interactions are covered in this work. The knowledge gained can be used to specifically optimize formulations and manufacturing processes. Furthermore, PUHDs systems based on other hybrid components, such as acrylate diols, can also benefit from the findings of this work.